1. Technical Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine and a laser printer, and more particularly, to an image forming apparatus which is provided with a plurality of paper feed openings capable of setting sheets of different sizes (including a sheet of the same size set in different feeding directions, i.e., longitudinal and lateral directions) for automatically selecting an optimum size of sheet among the sheets set in the plurality of sheet feeding openings corresponding to the relation between the size of an original and copying magnification.
2. Description of Related Art
A variety of this sort of image forming apparatuses have heretofore been proposed and put in practical use. For instance, there is an apparatus which is arranged to give a warning to a user in the case where a sheet of the optimum size to be selected is not set. In such an apparatus, a sheet of selected size can be set quickly in response to the warning so that an image forming operation on a sheet of the optimum size can be accomplished.
In such a conventional apparatus, however, no indication is made to which paper feed opening the selected size of sheet has to be set. The user thus simply selects a paper feed opening to which the sheet can be easily set. However, when all the paper feed openings are used for sheet accommodation, the selected sheet of the optimum size can not be set unless a sheet already set in one of the paper feed openings is removed. At this stage, a trouble happens if a wrong sheet is removed. It may happen, for instance, that a sheet which is frequently used is replaced with said optimum size of sheet. In such a case, there is a high probability that the sheet in frequent use has to be replaced again with the optimum size of sheet after an image forming operation has been completed. If the sheet in frequent use is removed from a paper feed opening and is left out of the opening, the sheet has to be set again in the paper feed opening upon receiving a warning after image forming operation has started whereby the image forming operation can not be carried out smoothly.
There is another case that a large number of sheets set in a paper feed opening is replaced with a sheet of the optimum size. In such a case, the large number of sheets weighs heavily and it is troublesome to replace them again. It is improper to leave the large number of sheets out of the apparatus.